2000 Honda CRV Barely runs

Water pump was leaking. Replaced water pump and timing belt. Checked and adjusted valves. Three bad motor mounts. Replaced those. Could not replace "rear" mount between engine and firewall as could not get in there to undo bolts. Engine starts fine. After a few seconds races up to 1200 rpm then settles down to 1000 rpm, when you press on throttle pedal rpm drops to 500 or less but engine does not die. Wait for a bit engine revs back to 1200 then 1000 and if you feather pedal then you can put in gear, rev up and move car. If you let foot up from pedal, rpm drops to 500 or less after few seconds will rev back up to 1200 then 1000. Engine never really dies completely. All this happen whether engine is warm or cold. Went through my work as far as checking cam position and rotor position at TDC along with pointer on harmonic balancer and everything seems fine. Wires are correct from plugs to distributor. Checked vacuum lines and did a test that was in my (Haynes) manual to verify no vacuum leaks, but could find nothing wrong. Replaced the IAC valve which did not help. When I was trying to get at the rear motor mount I tried to remove the tank that is on the rear firewall. I could not get the hoses off. If that was damaged in anyway would that be the problem. Have a lot of mechanical experience on heavy equipment and large generators ( 2.2 megawatt), but this is driving me nuts. In our little town, Haines, Alaska, no one seems to have a good solution either. Thank you for your time.